Gum arabic, the tree sap in your soda, stamps and watercolours
The glue on an old postage stamp, the gloss on M&M's, the binder in a box of watercolours and the stabiliser in soft drink syrup can all come from the same place: hardened sap oozing from acacia trees across Africa's Sahel. About 70% of the world's supply comes from Sudan.
Gum arabic is the dried exudate from the trunks and branches of two acacia species, Senegalia senegal and Vachellia seyal, though the name does not tie it to one botanical source. Chemically it is a tangle of glycoproteins and sugars, mostly chains of arabinose and galactose. It dissolves in water, is edible and acts as a natural glue. Collected in Arabia and West Asia since antiquity, it also became a prized export from the belt of acacia that once stretched across the Sahel from the Atlantic to the Red Sea.
Food makers label it E414 and use it to thicken, stabilise and emulsify icing, fillings, chewing gum and sweets, and to hold flavourings in soft drinks. Bartenders use gomme syrup, sugar and gum arabic dissolved in water, to stop sugar crystallising in cocktails. In the body it is not broken down in the stomach but fermented by microbes in the colon, which makes it a prebiotic fibre; large doses may simply cause flatulence.
Artists prize it too. In watercolour it suspends pigment and slows drying, allowing subtler washes, and with little water it binds colours more luminously. Lithographic printers use it to keep blank areas of a plate receptive to water and to protect aluminium plates from oxidation. The old gum bichromate photographic process mixed it with dichromate and pigment so that ultraviolet light fixed the image.
Its stickiness shows up in unexpected places: licking adhesive on envelopes and cigarette papers, shoe polish, incense cones, fireworks, and ceramic glazes, where it holds the glaze on unfired clay and then burns away without trace. Because its chemistry varies from batch to batch, more consistent substitutes have replaced it in some industrial uses.
Source: Gum arabic
